A power plant for large aircraft generally includes a turbofan, gas turbine engine and an associated nacelle for the engine. The nacelle extends circumferentially about the engine, sheltering the engine and providing aerodynamic surfaces which cooperate with the turbofan engine for generating thrust.
The turbofan engine includes a compression section, a combustion section and a turbine section. A primary flow path for working medium gases extends axially through the sections of the engine. An engine casing extends axially through the engine and circumferentially about the flowpath to bound the primary working medium flowpath.
The working medium gases of the primary flowpath are drawn into the compression section where they pass through several stages of compression, causing the temperature and pressure of the gases to rise. The gases are mixed with fuel in the combustion section and burned to form hot, pressurized gases. These gases are a source of energy to the engine and are expanded through the turbine section to produce work.
A secondary flowpath for working medium gases is disposed outwardly of the primary flowpath. The secondary flowpath is annular in shape. The engine has a plurality of fan blades which extend radially outwardly across the primary flowpath and secondary flowpath. These fan blades pressurize working medium gases entering both flowpaths of the engine.
The nacelle includes a fan nacelle and a core nacelle. The core nacelle is spaced from the engine leaving a core nacelle compartment therebetween which extends about the gas turbine engine. The core nacelle is disposed radially inwardly of the fan nacelle leaving a region therebetween for the secondary flowpath.
The core nacelle has an exterior wall and the fan nacelle has an interior wall which extend rearwardly to bound the secondary flowpath. Because the gases of the secondary flowpath flow over the walls of the nacelle, the walls are contoured to minimize the drag effect on high velocity gases in the working medium flowpath and to smoothly duct the gases along the flowpath.
The core nacelle compartment provides an enclosed shelter for engine accessories which are mounted on the exterior of the engine. These accessories might include fuel lines for flowing fuel to the combustion section; an electrical generator for supplying the engine and aircraft with electrical power; and a pneumatic duct for ducting a portion of the compressed gases of the engine through the nacelle and through struts to the aircraft. The gases in the pneumatic duct can have temperatures in excess of six hundred (600) degrees Fahrenheit. The gases may be used, for example, for controlling the environmental conditions of the aircraft and providing anti-icing gases to the aircraft. In addition, hydraulic conduits extend from the aircraft through the pylon into the nacelle. Hydraulic fluid is carried via these conduits to a hydraulic pump driven by the engine to pressurize the hydraulic fluid for use in various applications in the aircraft.
Three conduits are generally associated with each hydraulic system. A suction conduit supplies hydraulic fluid to the hydraulic pump from a tank in the aircraft. A pressure conduit supplies pressurized hydraulic fluid from the hydraulic pump to the aircraft hydraulic system at pressures as high as three thousand pounds per square inch. During operation of the pump, a small amount of hydraulic fluid is bypassed through the pump past seals and is used to lubricate components in the pump and for other functions. A case drain conduit, smaller in diameter than the supply conduit and pressure conduit, is used for returning this hydraulic fluid to the hydraulic fluid supply tank which is located in the aircraft.
Some of the components in the nacelle compartment, such as the hydraulic fluid, are affected by overheating. As will be realized, sources of heat include the engine and associated components, such as the pneumatic ducting and the hydraulic pump which does work on the hydraulic fluid. Accordingly, the nacelle compartment is ventilated during engine operation by cooling passages which flow a portion of the cool pressurized, air from the secondary flowpath to the interior of the nacelle.
One example of a cooling passage is an axially extending spray bar at the top of the nacelle. The spray bar flows cooling air into the upper region of the nacelle to ventilate the core nacelle compartment during operation of the engine.
Another example is shown U.S. Pat. No. 4,351,150 issued to Schulze entitled "Auxiliary Air System for Gas Turbine Engine" in which an air ducting pipe is used to duct cooling air to a component which generates heat, such as an electronic engine control, to cool the component. After cooling the control, the air is discharged into a compartment of the nacelle to provide ventilation to the compartment. Such systems may be used in a nacelle which is divided into many subcompartments, each isolated from the other.
Another example of a cooling and ventilating system used in a gas turbine engine nacelle is shown in U.S. Pat. No. 4,019,320 entitled "External Gas Turbine Cooling for Clearance Control" and U.S. Pat. No. 4,069,662 entitled "Clearance Control for Gas Turbine Engine", both issued to Redinger et. al. and assigned to the Assignee of this invention. In these constructions, cool air is bled from the fan discharge duct and is directed externally of the engine case into a region adjacent to seals in the turbine section of the gas turbine engine. Spray bars impinge the cooling air on the engine case to control the diameter of the case and internal operating clearances in the engine which are associated the position of the engine case. After the cool air impinges on the engine case, the air is flowed through the engine compartment to ventilate the compartment.
This cooling of the nacelle compartment is particularly important for hydraulic fluid which is flowed to the aircraft hydraulic system. The hydraulic fluid begins to deteriorate above a certain temperature and the amount of deterioration is a function of the time that it remains at that temperature.
Accordingly, scientists and engineers working under the direction of Applicants' Assignee have considered the impact of nacelle temperatures which result from operation of the aircraft and its gas turbine engine on the thermal life of the hydraulic fluid.